The present invention relates to a plasma-based process for the production of a dielectric rod from gaseous starting materials wherein the rod grows in the axial direction by deposition on its end face.
Such processes are used to manufacture high-purity glass materials or ceramic materials in rod form, especially preforms of quartz glass, from which optical waveguides are drawn for the communications industry.
Such processes are disclosed in the following references: DAS, No. 2,715,333; DOS No. 2,835,326; DOS No. 2,913,726; and DOS No. 2,919,619 (U.S. Pat. Nos. 4,062,665, 4,224,046, 4,231,774 and GB No. 1574115). all of whose disclosures are entirely incorporated by reference herein. These deal with the production of preforms from quartz glass having a gradient refractive index profile obtained by radially varied doping of the rod. The nozzle systems and nozzle movements required for this purpose, as well as the feeding of the doping material, form a large part and the main emphasis of these disclosures.
The advantage of the plasma method as compared with the flame hydrolysis method to achieve the desired growth has been recognized. In the plasma process, the nozzles are equipped, in part, with a plasma-generating device and are fashioned as plasma burners. In the prior art, the starting rod member, in most cases a round plate, is provided with a drive means which allows the rod to rotate during its manufacture.